The present invention relates to a sliding member and more particularly to a sliding member composed of resin, a sliding bearing unit comprising the sliding member and a developing apparatus comprising the sliding member.
There is a growing demand for the development of electrophotographic copying machines, printers, facsimiles and the like miniaturized, easy to operate, and inexpensive. In such a trend, a developing apparatus of process cartridge type which is compact, light, and easy to use, and removably installed inside electrophotographic copying machines, printers, facsimiles has been developed.
As a bearing device for use in the sliding portion of a developing apparatus, oil-contained and sintered sliding bearing unit and a sliding bearing unit composed of resin are increasingly used instead of a rolling bearing unit in recent years. The sliding bearing unit composed of resin is adopted more than the oil-contained and sintered sliding bearing unit because the former has a smaller degree of change in its sliding characteristic relative to the change in temperature than the latter.
Generally, the sliding bearing portion of the conventional sliding bearing unit composed of resin comprises a sliding member formed of synthetic resin impregnated with lubricating oil or comprises synthetic resin to which a lubricating component is added. For example, the former sliding member contains lubricating oil dispersed in the synthetic resin such as polyphenylene sulfide or polyacetal. The latter sliding member contains polytetrafluoroethylene or modified polyethylene mixed with the synthetic resin. For example, an aromatic polyamide resin composition which is processed into the sliding member and contains aromatic polyamide and modified polyethylene mixed therewith is known as disclosed in Laid-Open Japanese Patent Publication No. Hei3-285952.
The sliding bearing unit in which the bearing portion comprises the sliding member containing lubricating oil is most widely used because of its superior sliding characteristic.
The conventional sliding member and in particular, the sliding bearing unit composed of the synthetic resin impregnated with the lubricating oil, however, a problem that its sliding resistance increases with age. More specifically, in the conventional sliding bearing composed of the synthetic resin impregnated with the lubricating oil, frequently, the lubricating oil is held in the resin in the form of capsule. Thus, only the oil positioned in the surface layer of the resin contributes to the lubrication of the sliding bearing, whereas the oil positioned in the interior thereof does not contribute to the lubrication thereof. Consequently, the oil positioned in the surface layer of the resin composition decreases to the minimum, which may lead to seizing.
In particular, a bearing installed at both ends of the shaft of a photosensitive roller serving as a toner-carrying member or a latent image-holding member constituting a developing apparatus is prevented from rotating at a uniform speed due to fluctuation in sliding resistance with the elapse of time, thus making it difficult to form a preferable image. If a large motor is used in the developing apparatus to generate a great torque in order to prevent the photosensitive roller or the like from rotating at a nonuniform speed, it is difficult to produce a compact inexpensive developing apparatus.
The present invention has been made to solve the problems. It is accordingly an object of the present invention to provide a sliding member composed of resin and a sliding bearing unit both having a low degree of sliding resistance; and a developing apparatus comprising the sliding bearing unit and allowing the driving torque thereof to be small.
The present invention provide a sliding member composed of a molded resin composition, the composition comprising a synthetic resin, a polyolefin resin, and an oil.
The molded resin composition comprises that 0.5-30 parts by weight of the oil is added to 100 parts by weight of a resin comprising 100 parts by weight of the synthetic resin and 5-200 parts by weight of the polyolefin resin.
The polyolefin resin comprises at least one resin selected from the group consisting of polyethylenes and modified polyethylenes.
The oil comprises at least one oil selected from the group consisting of silicone oil and ester oil. Preferably, the oil consists of ester oil.
Preferably, the synthetic resin is a polyamide resin. Preferably, the polyamide resin is polycaprolactam or polylaulolactam.
Preferably, the resin composition further comprises an oil-preserving material and a pigment. Preferably, the pigment is a black pigment.
Another sliding member of the present invention composed of a molded resin composition, the composition comprising a polyamide resin having a chemical structure containing not less than 10 methylene units between amide bonds, and an oil.
The sliding member contains 100 parts by weight of the polyamide resin and 1-25 parts by weight of the oil.
Preferably, the polyamide resin is polylaulolactam.
The resin composition of the sliding member further comprises an oil-preserving material and a pigment such as a black pigment.
The sliding bearing unit of the present invention comprises the sliding member installed at the sliding bearing portion.
The sliding bearing unit can be preferably applied to a developing apparatus comprising an electrostatic latent image-forming means, a toner supply means, a developing means, and a transfer means.
In particular, the sliding bearing unit is constituted as a process cartridge.
As a result of their researches made on the oil preserving state and sliding characteristic of the sliding member composed of resin containing oil, the present inventors have found that the sliding member composed of the polyolefin resins and the oil has a low degree of initial sliding resistance and that the sliding resistance does not increase with age. This is attributed to the fact that the oil has a high degree of affinity for the polyolefin resins having methylene groups and dispersed uniformly in the sliding member composed of the resin containing the oil. That is, the oil is movably preserved in the sliding member. The present invention has been developed on the basis of such a discovery.
That is, the sliding member of the present invention has a structure in which the polyolefin resin and the oil coexist.
The polyamide or the like having a structure in which a large number of methylene groups having a preferable affinity for the oil is present in its molecules provides the superior sliding characteristics even though the polyolefins are not present therewith.
The sliding member of the present invention maintains its superior initial lubricating characteristics for a long time. Thus, the sliding bearing unit comprising the sliding member is reliable because seizing does not occur. The developing apparatus of the present invention allows the driving torque to be reduced because the sliding bearing unit is used at the shaft-supporting portion thereof. Consequently, developing apparatus forms a preferable image and can be allowed to be compact and light weight.